In its different modules (especially those for workflows), the JSU app supports many different field types. System fields, as well as custom fields.
However you should be aware, that not all field types are supported. Also not in all combinations. We think we cover the most important field types and still are continuously adding and improving which and how different field types are supported. But the one you need, might just not (yet) work. Some custom fields of other third party app might never get supported.
For that reason you should always test anything you do with the JSU app with fields. Before you buy a license for JSU, try it with a free evaluation license, if it works for you.